Passengers queue up for a security check at Pudong International Airport in Shanghai, China. The Transportation Security Administration is requiring passengers at some overseas airports that offer U.S.-bound flights to power on their electronic devices, the agency said Sunday. It says devices that won’t power up won’t be allowed on planes, and those travelers may have to undergo additional screening.

WASHINGTON — Passengers at some overseas airports that offer U.S.-bound flights will soon be required to power on their electronic devices in order to board their flights — a measure intended to enhance aviation security at a time when intelligence officials are concerned about hidden explosives, a counterterrorism official said.

American intelligence officials have been concerned about new al-Qaida efforts to produce a bomb that would go undetected through airport security. There is no indication that such a bomb has been created or that there’s a specific threat to the U.S., but intelligence has suggested that al-Qaida and like-minded groups are focused on perfecting an explosive that could be hidden in shoes, electronics or cosmetics, said the official who spoke on condition of anonymity because the official was not authorized to publicly discuss the matter.

The Transportation Security Administration says it is adding the requirement that passengers coming to the U.S. from some airports must turn on devices such as cellphones before boarding. It says devices that won’t power up won’t be allowed on planes and those travelers may have to undergo additional screening. Turning on an electronic device can show a screener that the laptop or cellphone, for instance, is a working device and that the batteries are used for operating that device and that the device is not hiding explosives.

The enhanced security measures come as U.S. intelligence officials are concerned about Americans and others from the West who have traveled to Syria to join the fight against the Syrian government. The fear is that a fighter with a U.S. or other Western passport, who therefore may be subject to less stringent security screening, could carry such a bomb onto an American plane.

TSA will not disclose which airports will be conducting the additional screening. Industry data show that more than 250 foreign airports offer nonstop service to the U.S.

Heathrow, Europe’s busiest airport, told passengers that they might not be allowed to take electronic devices onto planes if they could not be switched on.

It posted a security update on its website telling passengers, “If you are flying to the US please make sure any of your electronic devices are charged before you travel.”

British Airways also issued an update for passengers flying from Britain to the U.S. “Customers may be asked to turn on any electronic or battery powered devices such as telephones, tablets, e-books and laptops in front of security teams and/or demonstrate the item’s functionality,” the update said. “If, when asked to do so, you are unable to demonstrate that your device has power you will not be allowed to fly on your planned service.”

American intelligence officials have said that they have picked up indications that bomb makers from Yemen-based al-Qaida in the Arabian Peninsula have traveled to Syria to link up with the al-Qaida affiliate there.

Homeland Security Secretary Jeh Johnson recently ordered the TSA to call for extra security measures at some international airports with direct flights to the United States. TSA does not conduct screening abroad, but has the ability to set screening criteria and processes for flights flying to the U.S. from abroad, according to a Homeland Security Department official, who was not allowed to discuss the changes publicly and spoke on condition of anonymity.

During an interview aired Sunday on NBC’s “Meet The Press,” Johnson declined to speculate on whether new security procedures called for overseas will be required at domestic airports in the future.